Periodontal disease diagnosis supporting device, periodontal disease diagnosis supporting system, periodontal disease diagnosis supporting program, and periodontal disease diagnosis supporting method

ABSTRACT

In a test for supporting diagnosis of periodontal disease, a test method, whose measurement result has reproducibility and can be an objective index, is achieved and the loss of a tooth is predicted by use of the obtained objective index. A periodontal disease diagnosis supporting device supports diagnosis of periodontal disease by use of a captured three-dimensional image of a tooth part. The device includes a tooth root adhesion degree measuring part for measuring a degree of adhesion between a tooth root and alveolar bone by use of the image. The device further includes a periodontal disease diagnosis supporting part for supporting diagnosis of periodontal disease by use of a measurement result of the measuring part.

RELATED APPLICATIONS

This application is a U.S. Application which claims the benefit ofJapanese Application No. 2014-260353, filed Dec. 24, 2014. The contentsof all of these applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device, a system and a method forsupporting diagnosis of periodontal disease by use of a dental image,and especially relates to a device, a system, a program and a method forsupporting diagnosis of periodontal disease by measuring an attachmentlevel by use of a dental X-ray CT image.

2. Description of the Related Art

Periodontal disease is a disease generated by the progress of gingivitisand the spread of inflammation to periodontal tissues other thangingiva, and the disease involves progressive destruction of theperiodontal tissues. It is known that clinically, chronic inflammationof gingiva, bleeding from a periodontal pocket, regression of alveolarbone, and the like occur, and with the progress of destruction, a toothmoves or migrates, and is eventually lost naturally or required to beextracted.

In treatment of periodontal disease, it is necessary to first test towhat extent the current symptom has progressed, and then diagnose aresulting symptom that will subsequently occur. Test items forperiodontal disease include methods such as a mobility test, a bleedingand drainage test, an oral photograph test, a two-dimensional X-rayimage test and a bacteria test.

The mobility test is to test the degree of tooth mobility and roughlyclassify it into mobility levels 0 to 3. However, this test greatlyrelies on a subjective view of a test conductor, and further, during thetest, unnecessary external force may be applied to a tooth to causedamage thereto. The bleeding and drainage test is to performdetermination based on the occurrence or non-occurrence of bleeding anddrainage, but this cannot be an objective index of the degree ofprogress of periodontal disease.

In the oral photograph test, an overall oral state can be grasped, butthe degree of progress of periodontal disease cannot be objectivelydetermined. Also in the two-dimensional X-ray image (panoramic image)test, a state of alveolar bone, the presence or absence of tartar andthe like can be seen, but these are insufficient as objective indexes ofthe degree of periodontal disease.

The bacteria test is to test an abundance of pathogenic bacteria ofperiodontal disease, and such a method as a PCR (polymerase chainreaction) method is used. A result of the test may have effects onprediction of the onset and progress of periodontal disease, a treatmentmethod and the like, but this also cannot be an objective index of thedegree of periodontal disease.

In contrast to these, test methods whose results can be objectiveindexes include a periodontal pocket test, an attachment level test, andan alveolar bone resorption degree test.

The periodontal pocket test is also called a probing pocket depth testor the like, and is to measure a distance from the rim of gingiva to thetip of a periodontal probe at the time of inserting the probe into aperiodontal pocket. The measured value is similar to a value of ahistological pocket depth that is a distance from the rim of the gingivato the bottom of the pocket, but the measured value does not match thehistological pocket depth value. This is a simple method, but istroublesome as measurement is performed at about six spots (buccalmesial, central and centrifugal spots and lower mesial, central andcentrifugal spots) for one tooth. It may involve bleeding and inflictpain on a patient. Further, a test result varies depending on a testconductor, and is thus problematic as an objective index.

The attachment level test is to measure a distance from a cement-enameljunction (CEJ) to the tip of a periodontal probe at the time ofinserting the probe into a periodontal pocket, and normally, themeasured value is a value obtained by adding a gingiva regression amountto a probing pocket depth value. An attachment level means the positionof periodontal tissues attached to the tooth root surface, and is aresult of attachment loss from the past to the time of measurement. Anindex of a treatment effect is obtained by comparing the attachmentlevels before and after the treatment. Also in this test, the methodusing the periodontal probe has an equivalent problem to that in theperiodontal pocket test.

The alveolar bone resorption degree test is to measure an alveolar boneresorption degree expressed by a ratio of a distance of the resorbedalveolar bone (from the cement-enamel junction to the alveolar bonecrest) with respect to a tooth root length (from the cement-enameljunction to the root apex). This is considered to be the mostappropriate as an index indicating the degree of destruction of theperiodontal tissues such as the alveolar bone. In this test method,calculation is normally performed by analyzing a dental X-ray image or aclear panoramic X-ray image where a bone level can be identified.However, since this test method uses a two-dimensional X-ray image aseither of the above images, it cannot necessarily be said to be able tomeasure an appropriate distance, and the measured value cannot be anobjective index.

In regard to the periodontal disease test methods including the probingpocket depth test method and the alveolar bone resorption degree testmethod described above, a variety of proposals have hitherto been madeby prior literatures as cited below.

For example, Japanese Patent Laid-Open No. 2009-131313, which is herebyincorporated by reference, discloses a technical idea in which atomographic image of a periphery of a tooth part obtained using an OCTdevice is processed and a two-dimensional image is created to measure aheight of alveolar bone and a contour part of a periodontal pocket.However, in this technique using a laser light source, a depth of theperiodontal pocket hidden in gingiva is an estimated value, and cannotbe correctly measured, which is problematic. Further, a measurementmethod of this technique has a drawback of having great difficulties inoptical adjustment.

Moreover, Japanese Patent Laid-Open No. 2010-256190, which is herebyincorporated by reference, discloses a technical idea in which an amountof substance as Autoinducer-2 collected from plaque in a mouth of apatient is measured, to diagnose the degree of progress of periodontaldisease which has a correlation with the amount of Autoinducer. However,this case also has a drawback of having variations in result dependingon the plaque collecting position and a drawback of being unable toobtain an effective result in determination as to whether the degree ofprogress of periodontal disease corresponds to the whole or a localportion of the tooth.

In addition, a method for measuring a distance between a cement-enameljunction and the bottom of alveolar bone resorption (a depth of alveolarbone resorption) is described in “Automated method for measuringalveolar bone resorption by three-dimensional image processing”, NagaoJiro et.al., MEDICAL IMAGING TECHNOLOGY Vol. 25 No. 1, January 2007 (TheJapanese Society of Medical Imaging Technology). However, this issubstantially what can be put as measurement of an attachment level, andcannot be said to be sufficient in evaluating the degree of destructionof periodontal tissues as compared to measurement of an alveolar boneresorption degree.

As periodontal disease progresses, a tooth cannot be supported byperiodontal tissues such as alveolar bone, and the time of losing thetooth (by natural tooth extraction or tooth extraction treatment) comes.It has been expected that such time will become predictable if aquantitative test method is established. For example, Japanese PatentLaid-Open No. 2001-061873, which is hereby incorporated by reference,shows that the probability of losing a tooth increases by aging with ameasured attachment level taken as a reference, but this is based on avariety of hypotheses and the reliability of prediction cannot be saidto be sufficiently high.

It is to be noted that International Application PCT No. JP2013/067924,applied by the same applicant as that of the present application andunpublished on the filing date of the present application, describes atechnique concerning image processing that is used in the presentapplication.

SUMMARY OF THE INVENTION

As described above, the periodontal pocket test, the attachment leveltest and the alveolar bone resorption degree test are the test methodswhose measurement results have reproducibility and can be objectiveindexes in the test for supporting diagnosis of periodontal disease.However, especially the periodontal pocket test and the attachment leveltest which use the probe have the problem of variations in measurementresult depending on the test conductor, and some other problem.

Further, the alveolar bone resorption degree test capable of mostappropriately evaluating destruction of periodontal tissues has theproblem of slightly lacking the accuracy due to the use of atwo-dimensional X-ray image.

If an objective index is obtained, test results thereof can be collectedand analyzed in a broad range to predict the loss of a tooth, but anobjective index sustainable for such operation has not been established,which is problematic.

For solving the problems as thus described, the present inventionprovides a periodontal disease diagnosis supporting device whichsupports diagnosis of periodontal disease by use of a capturedthree-dimensional image of a tooth part, the device including a toothroot adhesion degree measuring part for measuring a degree of adhesionbetween a tooth root and alveolar bone by use of the image.

According to this, by use of the degree of adhesion between a tooth rootand alveolar bone, the occurrence or non-occurrence of periodontaldisease and the degree of progress thereof can be quantitativelygrasped, which is extremely effective for supporting diagnosis ofperiodontal disease. With the quantitative grasping being possible,accumulating temporal data of a person to be tested enables predictingthe progress of periodontal disease and the time of losing a tooth bydental tooth extraction or natural tooth extraction.

Further, in addition to the tooth root adhesion degree measuring part,the device may include a periodontal disease diagnosis supporting partfor supporting diagnosis of periodontal disease by use of a measurementresult of the measuring part.

According to this, by use of an objective index that is a tooth rootadhesion degree, it is possible to provide support information fordiagnosing the occurrence or non-occurrence of periodontal disease andthe degree of periodontal disease from the past case, the progress of apatient and the like.

Further, the tooth root adhesion degree measuring part may includemain-axis correction means for correcting an image by a main axisdefined by a unit vector of a line segment from center coordinates of atooth crown top to center coordinates of an entire tooth.

Herein, the tooth root adhesion degree measuring part may include

cement-enamel junction specifying means for specifying a cement-enameljunction,

alveolar bone crest specifying means for specifying an alveolar bonecrest, and

bone attachment level calculating means for calculating a boneattachment level from the specified cement-enamel junction and alveolarbone crest.

Herein, the bone attachment level is to show a distance between thecement-enamel junction and the alveolar bone crest of the tooth, and issynonymous with what was expressed as the “distance of the resorbedalveolar bone” in the above description. From this definition, anincrease in bone attachment level means a decrease in alveolar bonecrest, namely, resorption of the alveolar bone, and a large resorptiondegree of the alveolar bone means a decrease in length of contactbetween the tooth root and the alveolar bone and a decrease in degree ofadhesion therebetween. This supports diagnosis of the progress ofperiodontal disease or the tendency of losing the tooth in the future.Further, specifying the cement-enamel junction and the alveolar bonecrest in the image increases the possibility to obtain an objectiveindex that varies a little depending on an operator and hasreproducibility.

Herein, the tooth root adhesion degree measuring part may include

cement-enamel junction specifying means for specifying a cement-enameljunction,

alveolar bone crest specifying means for specifying an alveolar bonecrest,

root apex specifying means for specifying a root apex, and

tooth root adhesion length ratio calculating means for calculating atooth root adhesion length ratio that is a ratio of a distance betweenthe specified alveolar bone crest and root apex with respect to adistance between the cement-enamel junction and the root apex.

According to this, when the positions of the cement-enamel junction andthe alveolar bone crest are almost the same at the beginning, anumerical value of this ratio is 1, and as resorption of the alveolarbone progresses, the numerical value of the ratio decreases. Thus, theoccurrence or non-occurrence of periodontal disease and the degrees ofprogress thereof for different tooth parts, different people to betested and different times are indicated by numerical values between 1and 0, thereby allowing easy comparison and contrast.

Further, in the bone attachment level calculation, a bone attachmentlevel in a contact portion with a tooth adjacent to the tooth part to bemeasured may be calculated. According to this, it is possible tocalculate a bone attachment level in a contact portion where periodontaldisease rapidly progresses, thus helping to support early diagnosis ofperiodontal disease.

Further, the tooth root adhesion degree measuring part may include

tooth crown top specifying means for specifying a tooth crown top or atooth cervix specifying means for specifying a tooth cervix,

alveolar bone crest specifying means for specifying an alveolar bonecrest,

root apex specifying means for specifying a root apex, and

tooth root adhesion volume ratio calculating means for calculating atooth root adhesion volume ratio that is a ratio of a volume of a toothroot in an adhesion portion calculated from the specified root apex andalveolar bone crest with respect to a volume of an entire toothcalculated from the specified tooth crown top or tooth cervix and rootapex.

According to this, when the ratio of the volume of the adhesion portionbetween the tooth and the alveolar bone with respect to the volume ofthe entire tooth has decreased, it can be said that the tooth rootadhesion degree has decreased, thus supporting diagnosis of the progressof periodontal disease or the tendency of losing the tooth in thefuture.

Further, the tooth root adhesion degree measuring part may include

tooth crown top specifying means for specifying a tooth crown top or atooth cervix specifying means for specifying a tooth cervix,

alveolar bone crest specifying means for specifying an alveolar bonecrest,

root apex specifying means for specifying a root apex, and

tooth root adhesion surface area ratio calculating means for calculatinga tooth root adhesion surface area ratio that is a ratio of a surfacearea of a tooth root of an adhesion portion calculated from thespecified root apex and alveolar bone crest with respect to a surfacearea of an entire tooth calculated from the specified tooth crown top ortooth cervix and root apex.

According to this, when the ratio of the surface area of the adhesionportion between the tooth and the alveolar bone with respect to thesurface area of the entire tooth has decreased, it can be said that thetooth root adhesion degree has decreased, thus supporting diagnosis ofthe progress of periodontal disease or the tendency of losing the toothin the future.

Further, the device may include a periodontal disease progress statuspredicting part for predicting a progress status of periodontal diseaseby use of at least either a measurement result of the tooth rootadhesion degree measuring part or a diagnosis support result of theperiodontal disease diagnosis supporting part, and at least oneindividual attribute out of individual attributes which include an age,a sex, a medical history and current symptoms of diseases of an entirebody including dental diseases, a tooth-blushing habit, a smokinghistory, a drinking history, blood pressure, a blood-sugar level and apreference for food.

According to this, the progress status of periodontal disease, such asthe time of requiring tooth extraction, can be predicted in associationwith the individual attributes, and hence improvable items out of theindividual attributes can be guided for improvement, to sustain a ratioof the remaining teeth for a long period of time.

It should be noted that the technical ideas of the periodontal diseasediagnosis supporting device described above may be aspects of aperiodontal disease diagnosis supporting system including a dentalimaging device and an image display device. Further, those technicalideas may be aspects of a periodontal disease diagnosis supportingprogram independent of hardware.

In the periodontal disease diagnosis supporting device according to thepresent invention, diagnosis of periodontal disease is supported by useof a distance between a cement-enamel junction and an alveolar bonecrest, which can be objectively measured with high accuracy andreproducibility, thus allowing provision of highly reliable supportinformation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a periodontal disease diagnosis supportingsystem according to one embodiment of the present invention;

FIG. 2 is a schematic view of a tooth part for explaining the presentinvention;

FIG. 3 is a schematic view of a tooth part for explaining the presentinvention;

FIG. 4 is a diagram to explain operation of the periodontal diseasediagnosis supporting system according to one embodiment of the presentinvention;

FIG. 5 is an example of an image in the periodontal disease diagnosissupporting system according to one embodiment of the present invention;

FIG. 6 is an example of the image in the periodontal disease diagnosissupporting system according to one embodiment of the present invention;

FIG. 7 is an example of the image in the periodontal disease diagnosissupporting system according to one embodiment of the present invention;

FIG. 8 is an example of the image in the periodontal disease diagnosissupporting system according to one embodiment of the present invention;

FIG. 9 is an example of the image in the periodontal disease diagnosissupporting system according to one embodiment of the present invention;

FIG. 10 is an example of the image in the periodontal disease diagnosissupporting system according to one embodiment of the present invention;

FIG. 11 is an example of the image in the periodontal disease diagnosissupporting system according to one embodiment of the present invention;

FIG. 12 is a diagram to explain main-axis correction in a periodontaldisease diagnosis supporting device according to one embodiment of thepresent invention;

FIG. 13 is a view to explain a measurement cross section in theperiodontal disease diagnosis supporting device according to oneembodiment of the present invention;

FIG. 14 is an example of the image in the periodontal disease diagnosissupporting system according to one embodiment of the present invention;

FIG. 15 is a view to explain specification of a cement-enamel junctionin the periodontal disease diagnosis supporting device according to oneembodiment of the present invention; and

FIG. 16 is a view to explain specification of an alveolar bone crest inthe periodontal disease diagnosis supporting device according to oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, a periodontal disease diagnosis supporting systemaccording to one embodiment of the present invention will be describedwith reference to the drawings. It is to be noted that in the following,a range necessary for describing how to achieve the object of thepresent invention will be schematically shown, a range necessary fordescribing a portion corresponding to the present invention will bemainly described, and a portion whose description will be omitted issupported by a known technique.

FIG. 1 is a configuration diagram of a periodontal disease diagnosissupporting system 100 according to one embodiment of the presentinvention. As shown in this drawing, the periodontal disease diagnosissupporting system 100 includes a periodontal disease diagnosissupporting device 1 for supporting diagnosis of periodontal disease, athree-dimensional imaging device 2, and an image display device 3.

FIGS. 2 and 3 are schematic views of a tooth part for explaining thepresent invention. FIG. 2 shows a healthy tooth and its periphery, andFIG. 3 shows a tooth affected by periodontal disease and its periphery.A tooth 50 is configured of a tooth crown 51 as an upper part (in thecase of the lower jaw side) protruding from gingiva 57, and a tooth root52 as a lower part (in the case of the lower jaw side). A boundarybetween the tooth crown 51 and the tooth root 52 is a tooth cervix. Thetooth crown 51 has enamel 53 that covers its surface. The tooth root 52has hard cementum 54 that covers its surface, and is supported byalveolar bone 55, a periodontal ligament 56 and gingiva 57 which areperiodontal tissues.

Herein, a boundary between the cementum 54 and the enamel 53 is acement-enamel junction (CEJ) 58, and the top of the tooth crown 51 iscalled a tooth crown top 511, the tip (the lower end in the case of thelower jaw side) of the tooth root 52 is called a root apex 522, and thetop of the alveolar bone 55 is called an alveolar bone crest 554.Further, a distance between the cement-enamel junction 58 and thealveolar bone crest 554 is defined as a bone attachment level (BAL).

When the two drawings are compared, it is found that in the toothaffected by periodontal disease, the alveolar bone crest 554 has becomelower and a portion supporting the tooth root 52 has decreased. That is,there has been a decrease in degree of adhesion between the tooth root52 and the alveolar bone 55, the periodontal ligament 56 and the gingiva57 which are the periodontal tissues.

Returning to the periodontal disease diagnosis supporting system 100,the description will be continued. The periodontal disease diagnosissupporting device 1 is provided with an operation part 11, a CPU 12, amemory 13, a first interface 14 and a second interface 15, and these areconnected as in FIG. 1, for example. A form of the device is preferablya server or a personal computer, but it may be a form in which theseconstituents are connected wired and/or wirelessly, and may further be aform of a computer resource by a cloud using the Internet.

The operation part 11 is a keyboard, a mouse, a pointer or the likewhich allows input of characters and information such as an instructionon a screen. The operation part 11 may be a combination of a pluralityof those. In addition, the operation part 11 may not be necessarilyintegrated with the periodontal disease diagnosis supporting device 1,but may be connected using an interface.

The CPU 12 performs numerical value calculation, information processing,instrument control or the like by means of a program by an instructionfrom the operation part 11, or the like.

The memory 13 stores a program and data, and provides those according tothe need. Herein included as programs are a tooth root adhesion degreemeasuring part 20, a periodontal disease diagnosis supporting part 30and a periodontal disease progress predicting part 40.

The first interface 14 provides an interface with the three-dimensionalimaging device 2, and the second interface 15 provides an interface withthe image display device 3.

The three-dimensional imaging device 2 is a device capable of capturinga dental three-dimensional image, and is preferably an X-ray CT imagingdevice. The X-ray CT imaging device can capture a three-dimensionalimage of a dental region by means of an X-ray, to acquire volume data. Avariety of X-ray CT imaging devices have been put in practice, and anyof these can be employed. It is to be noted that the three-dimensionalimaging device 2 is not restricted to the X-ray CT imaging device, butis any device that can acquire volume data, such as a three-dimensionalsupersonic device, a nuclear magnetic resonance device, or a positronemission tomography device. It may be possible to provide appropriatediagnosis support in accordance with a characteristic of an imageobtained by the device.

The image display device 3 is a device capable of displaying an image,such as a liquid crystal display. The device is preferably capable ofmaking color display, but it may make monochrome display. A plasmadisplay other than the liquid crystal display can also be used. Itshould be noted that the image display device 3 may be configuredintegrally with the periodontal disease diagnosis supporting device 1 orthe operation part 11, or may be installed in a separate and remotemanner.

Further, the tooth root adhesion degree measuring part 20 includes, as aprogram, either or both bone attachment level calculating means 21or/and tooth root adhesion length ratio calculating means 22, andincludes, as means for the measurement, cement-enamel junctionspecifying means 23, alveolar bone crest specifying means 24 and rootapex specifying means 25.

Moreover, the memory 13 includes as a program the periodontal diseasediagnosis supporting part 30 for supporting diagnosis at the time ofdiagnosing the occurrence or non-occurrence of periodontal disease, thedegree of progress thereof and the like based on a measurement resultobtained by the tooth root adhesion degree measuring part 20.

Furthermore, the memory 13 includes the periodontal disease progresspredicting part 40 for predicting a progress status of the periodontaldisease by use of at least either a measurement result obtained by thetooth root adhesion degree measuring part 20 or a diagnosis supportresult obtained by the periodontal disease diagnosis supporting part 30,and at least one individual attribute out of individual attributes suchas an age, a sex, a tooth-blushing habit, a smoking history, a drinkinghistory, blood pressure, a blood-sugar level and a preference for food.

Herein, a description will be given of an action and operation of theperiodontal disease diagnosis supporting system 100 having theconfiguration as thus described. FIG. 4 is a diagram to explainoperation of the periodontal disease diagnosis supporting system 100according to one embodiment of the present invention.

<Imaging> (S10)

First, the three-dimensional imaging device 2 captures an image of theentire tooth row of a person who undergoes a test, (a person to betested), to acquire volume data.

<Specification of Measurement Target Tooth> (S11)

Next, the image display device 3 displays the captured image of theperson to be tested. FIG. 5 is one example of a tooth number screen atthe time of startup, and on this screen, a user specifies a tooth numberto be a measurement target. FIG. 6 is a screen after specification ofthe tooth number. With specification of the tooth number 4 (rightmaxillary second premolar) as the tooth number, there is displayed anyone image each of tomographic images in three directions concerning thistooth, namely an axial tomographic image (hereinafter, “A tomographicimage”), a coronal tomographic image (hereinafter, “C tomographicimage”) and a sagittal tomographic image (hereinafter, “S tomographicimage”). It is to be noted that in an initial state, the tomographicimages in the three directions display a central layer in the volumedata of the measurement target tooth. Generating a multi-sectionalreconstructed image from the volume data and displaying an A tomographicimage, a C tomographic image and an S tomographic image based on thegenerated image is a known technique, and its description will beomitted.

<Specification of Center Coordinates of Tooth Crown Top> (S12)

Next, the A tomographic image of the tooth is observed while thecross-sectional position is sequentially changed, to select an imagewhere a tooth crown can be observed. FIG. 7 shows an enlarged imagewhere the tooth crown can be observed. Since the A tomographic image,the C tomographic image and the S tomographic image are linked to oneanother, the user is allowed to specify the center position of the toothcrown top in the S tomographic image on the screen where the tooth crowncan be observed in the A tomographic image. FIG. 8 shows a screen in astate where the center of the tooth crown top has been specified.

<Specification of Center Coordinates of Entire Tooth> (S13)

Next, center coordinates of the entire tooth is specified in a similarprocedure to that for the center coordinates of the tooth crown top.First, as shown in FIG. 9, the center coordinate position of the entiretooth is allowed to be specified in the S tomographic image. Then, thecoordinate position is also displayed in each of the A tomographic imageand the C tomographic image. In this example, the center coordinates ofthe entire tooth are found displaced to the right in the A tomographicimage, and hence an appropriate position for the center coordinates isnewly allowed to be specified in the A tomographic image. FIG. 10 showsthis status.

<Setting of Region of Interest> (S14)

When the center coordinates of the entire tooth are specified, a cubicregion centered on the center coordinates of the entire tooth isdisplayed as shown in FIG. 11. This region indicates a region ofinterest of the measurement target tooth. This region can be enlargedand reduced by the operation part 11, and the smaller the size of theregion, the faster the image processing speed. However, any size can beset so long as the region includes a contact part with an adjacent toothand the size is not excessively large.

<Correction of Main Axis> (S15)

Next, by an instruction from the operation part 11, the image is rotatedby main-axis correction means such that a main axis, which connects thecenter of the tooth crown top and the center of the tooth part in theregion of interest, is vertical on the display. FIG. 12 shows aconceptual diagram of this operation. A specific technique is shown inInternational Application PCT No. JP2013/067924.

<Specification of Measurement Cross Section> (S16)

Next, a measurement cross section including the main axis is specified.While the measurement cross section can be set in any position within360 degrees, as an example conforming to a probing test method(six-point method), the measurement cross section is set at six pointsshown in FIG. 13 (#1: buccal contact part on the centrifugal surface,#2: middle point of #1 and #3, #3: buccal contact part on the mesialsurface, #4: lingual contact part on the mesial surface, #5: middlepoint of #4 and #6, #6: lingual contact part on the centrifugalsurface). Further, the most desirable cross section is a cross sectionincluding a contact portion that is the contact part with the adjacenttooth where the earliest progress of periodontal disease appears.

<Specification of Cement-Enamel Junction> (S17)

FIG. 14 shows the A tomographic image including the center of the toothcrown top, and measurement cross sections obtained by dividing aperiphery of the A tomographic image into six parts. On each of thesemeasurement cross sections, the cement-enamel junction is specified bythe cement-enamel junction specifying means 23. The cement-enameljunction appears as a boundary between enamel with high brightness andcementum with low brightness on the screen, and hence the user isallowed to specify that portion from the operation part. It is to benoted that the measurement cross section can be enlarged and displayedaccording to the need, to facilitate specification of the cement-enameljunction. FIG. 15 shows a specific specification procedure.

<Specification of Alveolar Bone Crest> (S18)

On the same screen as the measurement cross section where thecement-enamel junction is specified, an alveolar bone crest is specifiedby the alveolar bone crest specifying means 24. The alveolar bone isalso displayed with high brightness in gingiva with low brightness, andcan thus be easily distinguished, and its crest is also clear. Theoperator is allowed to specify this portion from the operation part.FIG. 16 shows a specific procedure for specification of the alveolarbone crest.

<Calculation of Bone Attachment Level> (S18)

When specification of the cement-enamel junction and the alveolar bonecrest is completed, a bone attachment level is calculated by the boneattachment level calculating means 21. Specifically, as shown in FIG.16, the cement-enamel junction and the alveolar bone crest are connectedby a straight line, to obtain a distance therebetween by calculation onthe screen.

<Specification of Root Apex> (S19)

Moreover, a root apex being the end of a tooth root part is allowed tobe specified on the same displayed cross section by the root apexspecifying means 25. Tissues of the tooth root part and tissuestherearound have different compositions, thus making a difference inbrightness therebetween, and hence the tooth root part can be easilydistinguished. The operator is allowed to specify this portion from theoperation part.

<Calculation of Tooth Root Adhesion Length Ratio> (S20)

Subsequently, in the tooth root adhesion length ratio calculating means22, “(distance between alveolar bone crest and root apex):(distancebetween cement-enamel junction and root apex)” is calculated.Specifically, each of the distances is calculated from the positions ofthe cement-enamel junction, the alveolar bone crest and the root apex,and a ratio of the distances is obtained.

<Support of Periodontal Disease Diagnosis> (S21)

In the periodontal disease diagnosis supporting part 30, the numericalvalue of the bone attachment level or the tooth root adhesion lengthratio as the index of the tooth root adhesion degree as has beendescribed is checked with a determination reference for periodontaldisease, to provide information that supports diagnosis. As thedetermination reference for periodontal disease, there can be consideredsuch a reference as the bone attachment level being not larger than astandard value or a decrease in bone attachment level from the normaltime being not smaller than a reference value. Further, as for the toothroot adhesion length ratio, such a reference as 0.7 or lower can beconsidered, but settings of these references ultimately rely ondiagnosis by a doctor.

<Prediction of Progress of Periodontal Disease> (S22)

Further, in the periodontal disease diagnosis predicting part 40,information related to the health of the person to be tested is comparedwith the numerical value of the bone attachment level or the tooth rootadhesion length ratio, to predict the progress of periodontal diseasebased on data stored up to the current. For example, the time when toothextraction is required, or the time when tooth is naturally extractedafter being left untreated, is estimated. Herein, the informationrelated to the health of the person to be tested includes individualattributes in addition to results of a variety of periodontal tests. Theindividual attributes include an age (a factor due to aging), a sex (adifference due to a different sex being a male or a female, an influenceof pregnancy), a medical history and current symptoms of diseases(diabetes, osteoporosis, heart disease, cerebral vascular disease, etc.)of an entire body, including dental diseases, for the person and his orher family, a tooth-brushing habit, a smoking history, a drinkinghistory, blood pressure, a blood-sugar level, a preference for food andthe like.

<Calculation of Tooth Root Adhesion Volume Ratio>

As the tooth root adhesion degree measuring part, tooth root adhesionvolume ratio calculating means may be used in conjunction with, or inplace of, the bone attachment level calculating means or the tooth rootadhesion length ratio calculating means described above. A tooth rootadhesion volume ratio (Kv) can be calculated in a following manner.Herein, before calculation of the tooth root adhesion volume ratio (Kv),first, a volume (VF) of the entire tooth is calculated as follows. Aroot apex is specified by the root apex specifying means, and the toothcrown top is specified by tooth crown top specifying means. Next, avolume from the root apex to the tooth crown top is taken as the volume(VF), and this is calculated. For example, using an X-ray CT image, acontour is automatically detected and its area is calculated. This iscontinued from the root apex to the tooth crown top, and a total sum istaken as the volume (VF). The area is the number pixels surrounded bythe contour. The number of pixels surrounded by the contour isintegrated. This is converted to an actual unit. In this case, thevolume (VF) of the tooth can be calculated by Mathematical Formula 1. Itis to be noted that symbol “SUR” in Mathematical Formula 1 denotes anarea in a contour of the tooth on a (x, y)-coordinate plane with az-coordinate being z, symbol “HA” denotes a z-coordinate of the rootapex, and symbol “HC” denotes a z-coordinate of the tooth crown top. Thesame applies to the following. The volume (VF) of the tooth may beobtained by integrating the number of pixels and converting the obtainedvalue to an actual unit.

$\begin{matrix}{V_{F} = {\int_{HA}^{HC}{{z}\underset{SUR}{\int\int}{x}{y}}}} & \left\lbrack {{Mathematical}\mspace{14mu} {Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Next, a volume (VC) of the tooth root surrounded by the alveolar bonecurrently supporting the tooth is calculated as follows. An alveolarbone crest is specified by the alveolar bone crest specifying means.Subsequently, a region from the alveolar bone crest to the root apex,surrounded by the alveolar bone, is calculated as a volume (VC) of thetooth root. In this case the volume (VC) of the tooth root surrounded bythe alveolar bone can be calculated by Mathematical Formula 2. It shouldbe noted that symbol “HB” denotes a z-coordinate of the alveolar bonecrest.

$\begin{matrix}{V_{C} = {\int_{HA}^{HB}{{z}\underset{SUR}{\int\int}{x}{y}}}} & \left\lbrack {{Mathematical}\mspace{14mu} {Formula}\mspace{14mu} 2} \right\rbrack\end{matrix}$

The tooth root adhesion volume ratio (Kv) can be calculated by the toothroot adhesion volume ratio calculating means as a ratio (VC/VF) of thevolume (VC) of the tooth root surrounded by the alveolar bone currentlysupporting the tooth with respect to the total volume (VF) of the tooth.That is, the tooth root adhesion volume ratio (Kv) can be calculated byMathematical Formula 3.

K _(V) =V _(C) /V _(F)   [Mathematical Formula 3]

A value of the tooth root adhesion volume ratio is from 0 to about 0.5,and becomes a large value in a healthy state. For example, KV down toabout 0.4 is considered to indicate the healthy state. This value 0.4 isa provisional value, and the minimum value for the healthy state willhereafter be verified based on a large number of examples and decided.Based on the ratio as thus calculated, diagnosis of periodontal diseasecan be supported.

If the displayed image is appropriately set, the user is allowed to veryeasily specify the tooth crown top, the tooth cervix, the root apex andthe alveolar bone crest on the image, and thus allowed to select asappropriate a plurality of places therearound to manually performselection. An adhesion volume can be easily calculated therefrom,leading to obtainment of an objective index by the user, the indexvarying a little depending on the user and having reproducibility.

<Calculation of Tooth Root Adhesion Surface Area Ratio>

As the tooth root adhesion degree measuring part, tooth root adhesionsurface area ratio calculating means may be used in conjunction with, orin place of, the bone attachment level calculating means, the tooth rootadhesion length ratio calculating means or the tooth root adhesionvolume ratio calculating means described above. A tooth root adhesionsurface area ratio (KS) can be calculated in a following manner. A rootapex is specified by the root apex specifying means, a tooth crown topis specified by the tooth crown top specifying means, and an alveolarbone crest is specified by the alveolar bone crest specifying means.First, a tooth root surface area (S) can be calculated by MathematicalFormula 4. For calculating a total surface area (SF) of the tooth, anintegration upper limit of the formula is taken as the tooth crown top,and for calculating a surface area (SC) of the tooth root surrounded bythe alveolar bone, an integration upper limit of the formula is taken asthe alveolar bone crest. The tooth root surface area can be substitutedby a value obtained by integrating a length of the contour in the X-rayCT image. Strictly speaking, the tooth root surface area is not equal tothe length of the contour, but values of those are hardly different whencalculated in a strict manner, and hence the length of the contour canbe the substitute. It is to be noted that in Mathematical Formula 4,symbol “CON” denotes a region for calculating the length, namely acontour line of the tooth in a cross section along the (x, y)-coordinateplane with the z-coordinate being z.

$\begin{matrix}{S = {\int_{HA}^{HT}{{z}{\int\limits_{CON}{\sqrt{1 + \left( \frac{y}{x} \right)^{2}}{x}}}}}} & \left\lbrack {{Mathematical}\mspace{14mu} {Formula}\mspace{14mu} 4} \right\rbrack\end{matrix}$

The tooth root adhesion surface area ratio (KS) can be calculated from aratio (SC/SF) of the surface area (SC) of the tooth root surrounded bythe alveolar bone currently supporting the tooth with respect to thetotal surface area (SF) of the tooth calculated from the above. That is,the tooth root adhesion surface area ratio (KS) can be calculated by thetooth root adhesion surface area ratio calculating means by MathematicalFormula 5.

K _(S) =S _(C) /S _(F)   [Mathematical Formula 5]

The tooth root adhesion surface area ratio (KS) also takes a value from0 to about 0.5, and the larger the value, the healthier the state. Basedon the ratio as thus calculated, diagnosis of periodontal disease can besupported.

It is to be noted that in calculating the tooth root adhesion volumeratio and the tooth root adhesion surface area ratio, the tooth cervixmay be used in place of the tooth crown top. This may be effective inevaluation of the difficulty level of specification or the calculatedratio. The tooth cervix is specified by searching a curvature changingpoint along a curve of the side surface of the tooth and taking theobtained curvature changing point as the tooth cervix.

Further, if the displayed image is appropriately set, the user isallowed to very easily specify the tooth crown top, the tooth root andthe alveolar bone crest in the image, and thus allowed to select asappropriate a plurality of places therearound to manually performselection. An adhesion surface area can be easily calculated therefrom,leading to obtainment of an objective index by the user, the indexvarying a little depending on the user and having reproducibility.

It is to be noted that in the above description, the user has beenallowed to perform specification by the means such as the cement-enameljunction specifying means, the alveolar bone crest specifying means, theroot apex specifying means, the tooth crown top specifying means and thetooth cervix specifying means. However, characteristics on a screen maybe identified by a program and specification may be automaticallyperformed. In that case, it is possible to perform specification on theentire periphery of the tooth part instead of selecting a plurality ofplaces and performing specification.

Further, a single rooted tooth having a single tooth root has beenassumed in the above description, but the above embodiment is alsoapplicable to a multiple rooted tooth having a plurality of tooth roots.For example, as for calculation of a bone attachment level, thecalculation is possible irrespective of the number of tooth roots.

Also as for calculation of a tooth root adhesion length ratio of amultiple rooted tooth, for example, a molar has three tooth roots, andhence the calculation is possible by defining, as a ratio to beobtained, an average of measured values of tooth root adhesion lengthratios on three different cross sections each including a main axis andeach root apex. In addition, for calculation of the tooth root adhesionlength ratio of the multiple rooted tooth, the above definition may notbe used. The tooth root adhesion length ratio may be defined by themaximum or minimum of the tooth root adhesion length ratios instead ofthe average thereof, or it may be defined by use of an appropriate rootapex or a place as a substitute for the root apex on the cross sectionincluding a contact portion with an adjacent tooth.

Also as for a tooth root adhesion volume ratio and a tooth root adhesionsurface area ratio of the multiple rooted tooth, those ratios can beobtained by a method of integrating a distance from the root apex in thedeepest part out of the plurality of root apexes to an alveolar bonecrest or a tooth crown top.

In addition, the present invention has been described above as theperiodontal disease diagnosis supporting device, system and program, butthe technical idea according to the present invention can naturally berealized as a periodontal disease diagnosis supporting method.

DESCRIPTION OF SYMBOLS

-   1 periodontal disease diagnosis supporting device-   2 three-dimensional imaging device-   3 image display device-   11 operation part-   12 CPU-   13 memory-   14 first interface-   15 second interface-   20 tooth root adhesion degree measuring part-   21 bone attachment level calculating means-   22 tooth root adhesion length ratio calculating means-   23 cement-enamel junction specifying means-   24 alveolar bone crest specifying means-   25 root apex specifying means-   30 periodontal disease diagnosis supporting part-   40 periodontal disease progress predicting part-   50 tooth-   51 tooth crown-   511 tooth crown top-   52 tooth root-   522 root apex-   54 cementum-   55 alveolar bone-   554 alveolar bone crest-   58 cement-enamel junction-   100 diagnosis supporting system

What is claimed is:
 1. A periodontal disease diagnosis supporting devicewhich supports diagnosis of periodontal disease by use of a capturedthree-dimensional image of a tooth part, the device comprising: a toothroot adhesion degree measuring part for measuring a degree of adhesionbetween a tooth root and alveolar bone by use of the image.
 2. Theperiodontal disease diagnosis supporting device according to claim 1,comprising a periodontal disease diagnosis supporting part forsupporting diagnosis of periodontal disease by use of a measurementresult of the tooth root adhesion degree measuring part.
 3. Theperiodontal disease diagnosis supporting device according to claim 1,wherein the tooth root adhesion degree measuring part includes main-axiscorrection means for correcting an image by a main axis defined by aunit vector of a line segment from center coordinates of a tooth crowntop to center coordinates of an entire tooth.
 4. The periodontal diseasediagnosis supporting device according to claim 1, wherein the tooth rootadhesion degree measuring part includes cement-enamel junctionspecifying means for specifying a cement-enamel junction, alveolar bonecrest specifying means for specifying an alveolar bone crest, and boneattachment level calculating means for calculating a bone attachmentlevel from the specified cement-enamel junction and alveolar bone crest.5. The periodontal disease diagnosis supporting device according toclaim 1, wherein the tooth root adhesion degree measuring part includescement-enamel junction specifying means for specifying a cement-enameljunction, alveolar bone crest specifying means for specifying analveolar bone crest, root apex specifying means for specifying a rootapex, and tooth root adhesion length ratio calculating means forcalculating a tooth root adhesion length ratio that is a ratio of adistance between the specified alveolar bone crest and root apex withrespect to a distance between the cement-enamel junction and the rootapex.
 6. The periodontal disease diagnosis supporting device accordingto claim 4, wherein the bone attachment level calculating meanscalculates the bone attachment level in a contact portion with a toothadjacent to the tooth part to be measured.
 7. The periodontal diseasediagnosis supporting device according to claim 1, wherein the tooth rootadhesion degree measuring part includes tooth crown top specifying meansfor specifying a tooth crown top or a tooth cervix specifying means forspecifying a tooth cervix, alveolar bone crest specifying means forspecifying an alveolar bone crest, root apex specifying means forspecifying a root apex, and tooth root adhesion volume ratio calculatingmeans for calculating a tooth root adhesion volume ratio that is a ratioof a volume of a tooth root in an adhesion portion calculated from thespecified root apex and alveolar bone crest with respect to a volume ofan entire tooth calculated from the specified tooth crown top or toothcervix and root apex.
 8. The periodontal disease diagnosis supportingdevice according to claim 1, wherein the tooth root adhesion degreemeasuring part includes tooth crown top specifying means for specifyinga tooth crown top or a tooth cervix specifying means for specifying atooth cervix, alveolar bone crest specifying means for specifying analveolar bone crest, root apex specifying means for specifying a rootapex, and tooth root adhesion surface area ratio calculating means forcalculating a tooth root adhesion surface area ratio that is a ratio ofa surface area of a tooth root in an adhesion portion calculated fromthe specified root apex and alveolar bone crest with respect to asurface area of an entire tooth calculated from the specified toothcrown top or tooth cervix and root apex.
 9. The periodontal diseasediagnosis supporting device according to claim 1, comprising aperiodontal disease progress status predicting part for predicting aprogress status of periodontal disease by use of a measurement result ofthe tooth root adhesion degree measuring part, and at least oneindividual attribute out of individual attributes which include an age,a sex, a medical history and current symptoms of diseases of an entirebody including dental diseases, a tooth-blushing habit, a smokinghistory, a drinking history, blood pressure, a blood-sugar level and apreference for food.
 10. The periodontal disease diagnosis supportingdevice according to claim 2, comprising a periodontal disease progressstatus predicting part for predicting a progress status of periodontaldisease by use of a diagnosis support result of the periodontal diseasediagnosis supporting part, and at least one individual attribute out ofindividual attributes which include an age, a sex, a medical history andcurrent symptoms of diseases of an entire body including dentaldiseases, a tooth-blushing habit, a smoking history, a drinking history,blood pressure, a blood-sugar level and a preference for food.
 11. Aperiodontal disease diagnosis supporting system, comprising: theperiodontal disease diagnosis supporting device according to claim 1; athree-dimensional imaging device for capturing a three-dimensional imageconcerning a tooth part; and an image display device for displaying animage from at least either the periodontal disease diagnosis supportingdevice or the three-dimensional imaging device.
 12. A periodontaldisease diagnosis supporting program which makes a computer executetooth root adhesion degree measuring means for measuring a degree ofadhesion between a tooth root and alveolar bone by use of a capturedthree dimensional image of a tooth part.
 13. The periodontal diseasediagnosis supporting program according to claim 11, wherein the computeris made to execute periodontal disease diagnosis supporting means forsupporting diagnosis of periodontal disease by use of a measurementresult of the tooth root adhesion degree measuring means.
 14. Aperiodontal disease diagnosis supporting method for supporting diagnosisof periodontal disease by use of a captured three-dimensional image of atooth part, the method comprising: measuring a degree of adhesionbetween a tooth root and alveolar bone by use of the image; andsupporting diagnosis of periodontal disease by use of a measurementresult of the tooth root adhesion degree.